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The Nobel Prized Piece of Glass

Optical fibres and CCD arrays were both awarded the 2009 Nobel Prize in physics. Finally, a Nobel Prize with some relevance to something you and I depend on every day!

Colladons ljusfontän / Colladon’s light fountain

There can be no doubt as to why the optical fibre received the Nobel Prize: it easily fulfils Alfred Nobel’s requirements for a discovery that is of immediate use to mankind. This is how the Nobel committee formulated their decision: The 2009 Nobel Prize in Physics is awarded for two scientific achievements that have helped to shape the foundations of today’s networked societies. They have created many practical innovations for everyday life and provided new tools for scientific exploration.

The phenomenon that light will stay inside a transparent conductor by bouncing off the walls was discovered as early as 1842 by the scientist Daniel Colladon. In that time it was mostly a scientific curiosity without any connection to communication. Anyway, Colladon had properly grasped the phenomenon. During the years 1920-1930 optical conductors were beginning to be used for lighting up the inside of the human body (fibre scopes) as well as in dentistry. The semi-flexible gastroscope appeared in 1956.

Charles K Kao. Bild / Image: Nobelstiftelsen

After that, optical communication came into play. The Japanese researcher Jun-ichi Nishizawa at the University of Tohoku in 1963 suggested that optical fibres could be used for communication, but the first optical link didn’t se the light of dawn until 1965, then demonstrated by the physicist Manfred Börner at the Telefunken research laboratory in Ulm in Germany. The attenuation of these fibres was probably somewhere around 20 dB/km, which would have prevented long-distance communication.

The Nobel Prize laureate Charles K Kao simply got the right ideas at the right time. In 1966 he was doing material research on glass and fibres at the Standard Telecommunication Laboratories in Harlow in England. He realised that if one could eliminate the iron ions in the glass (the substance that stains beer bottles green) and determine the proper wavelength, that is, between 1300 – 1550 nanometres, and use single mode to eliminate light bouncing inside the fibre, one could reach attenuations below a few decibels per kilometre. With that achieved, long-distance communication would indeed become possible.

He had the right idea but it would take another couple of years before industry managed to make glass that was clear enough. In 1969, Corning Glass Works in the U.S. succeeded to create a cladded fibre, citing direct inspiration from one of Kao’s articles. The fibre had a glass core doped with titanium and used pure silicon dioxide for cladding (surface layer). As Kao had proposed, an attenuation below one decibel per kilometre was soon achieved.

The rest is, as we say, history. Today we couldn’t exist without optical fibres.

You may not appreciate exactly how clear the glass in an optical fibre actually is. Imagine a typical folding glass wall, as used in most shopping malls. After one has folded ordinary window glass to a thickness of about 30 centimetres it is more or less opaque. Had the glass been made of optical fibre quality, you could have a window one kilometre thick and you would still have been able to see through it. That’s some difference.

In practice, in today’s SUNET, the fibre we use exhibits less than 0.22 decibels of attenuation per kilometre. This means we can have about 80 kilometres of fibre before the light is attenuated enough to require amplification. Read more in the article about optical magic with EDFA amplifiers: ”Teknisk djupdykning: Optisk magi med EDFA”.